I would say yes a percheron could live on one acre. But is it a full acre just for the horse or is it a one acre lot with a house, yard, and small pasture? It is very possible that a horse that big will stomp out most of the plant life on one acre.
A 3 sided run in is always good. They sell them as kits anywhere you can buy livestock panels.
No a standard rope halter will not fit. Not even close. You will need a draft halter. You will need bigger everything.
Please keep in mind that the bigger they are the more they cost to keep. Just having her feet trimmed can cost you quite a bit and if you have shoes put on her you'll be paying 3-5x the amount you would for a standard size horse.
Not trying to discourage you, just make sure you go in with both eyes open.
Post pics if you get her.
Riding: The art of keeping a horse between you and the ground. ~Author Unknown